What is a “feral” cat, anyway?
“Feral“ animals are members of domesticated species (such as cats, dogs, or horses) that have reverted to a wild state. When we speak of feral cats, we’e usually talking about the offspring of unspayed/unneutered pet cats who strayed from home or were abandoned. These kittens are born outdoors and don't have any contact with humans, so they grow up “unsocialized“—basically, they’re wild animals, just like squirrels or raccoons. This differentiates them from “stray” cats—former pets who once had a home but were either lost or abandoned.
Feral cats are usually very fearful of humans. They cannot be petted or picked up, and will definitely swat or bite if they feel threatened or cornered, just like any other wild animal. But mostly they just want to stay as far away from people as possible.
Feral kittens who are rescued before 8-10 weeks of age can usually be socialized and become friendly to people, and occasionally older kittens and cats can become somewhat socialized. But this is a VERY long and intensive process. For this reason, it is impossible to place adult feral cats into pet adoption programs. Besides, feral cats already have a home—outside. That’s where they were born and have spent their whole lives. They generally manage to find reliable sources of food and shelter, where they’ll group together into colonies.
The concept of trap-neuter-return (TNR) was developed as a humane way to manage these colonies and prevent the breeding that leads to even more feral cats. With TNR, cats are caught with humane box traps, spayed/neutered and vaccinated, and then released back where they were found to live out their lives under the eye of a watchful human caretaker who provides food, water and shelter as necessary. Feral cats that have been “TNRed” are usually ear-tipped, meaning that the tip of one ear (usually the left) is clipped while the cat is under anesthesia. This makes it easier to visually identify TNRed cats from a distance after they’ve been released.
Spaying and neutering feral cats not only prevents more kittens from being born, but also reduces the nuisance behaviors often associated with feral colonies—spraying/marking by males, fighting, noisy mating encounters, etc.
Sometimes feral cats are living in an area that is unsafe or unsuitable, such as a building that is about to be demolished or near a busy road. Although it is always preferable to release feral cats back where they were living, in these instances a colony might have to be relocated. This is only done as a last resort and a period of acclimation, where the cats are kept confined in crates in their new territory, is required.
In general, humans have absolutely nothing to fear from feral cats. They do not “attack” people; in fact, most want nothing to do with people at all. (Although, like any wild animal, they might bite or scratch if they feel cornered and threatened.) Cats that have been TNRed are vaccinated for rabies, and usually one vaccination provides enough immunity for the lifespan of a typical feral cat.
Keep in mind that it can sometimes be difficult to tell if a cat is feral or not before it is trapped. Cats who live on the street often have lots of bad experiences with people, so even tame and friendly cats can come to assume that all humans mean them harm and become very fearful. And some tame cats are just naturally timid and shy. So don’t assume a cat is feral just because it runs away from you. This page from Alley Cat Allies helps illustrate the difference between stray cats and feral cats.